Gas measurement systems often require specifically designed gas cells to provide a well-defined flow of gas through the gas analyzer and to contain the sample gas in a sealed environment, separated from the environment of the analyzer. With regard to these criteria, gas cells must simultaneously meet several different and very demanding objectives, encompassing (1) aspects of gas supply, gas handling and material related issues, and (2) effects caused by the incorporation of the sample gas cell into the measurement system as they influence the operational properties of the analyzer.
To comply with gas supply, gas handling, and material related aspects of the gas measurement system, gas cells must meet the following criteria: (i) they must facilitate the supply of sample gas to the analyzer without exposing the analyzer to sample gas, thereby preventing contamination of sample gas with gas molecules present in the environment of the analyzer; and (ii) the materials comprising the gas cell and in contact with the sample gas, wetted materials hereafter, must be chemically inert with respect to the sample gas, thereby preventing contamination of the sample flowing in the gas cell.
To be compatible with the operational criteria of the gas measurement system, the gas cell incorporated into the analyzer must fulfill one of two general designs: (i) gas cells can be constructed in a way that they introduce minimal, or ideally, no alteration of the operational parameters of the measurement system, a design which is particularly demanding in the case of laser based optical devices; or (ii) gas cells can be constructed in a way that they sustain the operation of the analyzer while deliberately altering the performance parameters of the analyzer. The alteration of the analyzer performance is directly associated with properties of the gas cell itself, e.g., interference patterns caused by cell windows. This approach is often limited to a particular combination of gas cell and optical analyzer.
Regardless of the approach, internal geometry, sample volume and flow characteristics of the gas cell determine the timely response of the analyzer to sample gas concentration changes and can greatly influence the performance of the measurement system. Thus, the gas cell must be optimized in design to minimize response time of the analyzer while maintaining the other desired objectives.
A gas cell optimized for minimum alteration to the operation of the measurement system, complying with the requirements described in the previous sections and suitable for trace gas detection via intracavity laser spectroscopy (ILS) is described herein. Because of its unique and versatile design that minimizes detrimental optical effects within the gas measurement system, the range of potential applications for this gas cell can encompass virtually any optically based application involving gas detection or laser spectroscopy that requires a gas cell.